There exist a wide variety of techniques and systems that are known in the art for achieving the mixing or reactions of liquids with gases. In some cases, a simple bubble column is employed, with the injected gas rising up through the body of liquid in the tank. Upon injection, the oxygen, hydrogen, or other reactive gas either reacts directly when in bubble form, or dissolves in the liquid and then reacts, or both.
Stirred Tank Reactors (STR) are also commonly employed to enhance the gas-liquid mixing process. In an STR system, gas is normally fed to a sparger at the bottom of a vessel and a flat-bladed Rushton turbine or other such mechanical agitator is used to shear the gas for improved dispersion in the liquid phase. In addition, axial flow impellers are commonly employed in STR systems to facilitate gas dissolution.
In other gas-liquid mixing operations a down-pumping impeller positioned within a hollow draft tube in a mixing vessel is used to create a recirculation flow pattern of the liquid contained in the vessel. Because of such recirculation of the liquid downward in the hollow draft tube and upward in the vessel outside the draft tube, vortices are formed in the upper inlet area of the draft tube so as to draw feed gas from an overhead gas space within the vessel into the recirculating liquid passing downward into draft tube.
In many gas-liquid mixing applications, particularly those in the specialty chemical and pharmaceutical areas, the viscosity of the solutions tend to be higher than that of clean water and may tend to vary over time. In particular, mixing processes in the specialty chemical and pharmaceutical areas are often done under conditions of medium to high viscosity of the solution caused usually by the inclusion of solids in liquid flow (e.g. slurries), or by certain chemical characteristics of the liquids that cause exhibition of non-Newtonian fluid characteristics.
Prior art solutions to liquid-gas mixing for highly viscous solutions include the use of a plurality of mixers, nozzles or orifices to better disperse the gas within the viscous liquid, or alternatively, the forced circulation of the liquid in atomizers and spray nozzles. Disadvantageously, the additional equipment and process steps used in the mixing of highly viscous solutions often translate to consumption of larger amounts of energy. In addition, the inclusion of additional mixers, nozzles, atomizers, etc. may increase the footprint of the underlying process system as well as increase the capital and operating costs associated with the mixing process.